Nobody is ordering 6.4, 6.0, or 7.3L engines now since they have been out of production for years. However, there are quite a few 6.7L trucks in service. We have a pretty large trash company running a fleet of 20+ current-gen F-750 diesel trucks; our city's DPW runs a fleet of F-550 diesel dump truck / plow trucks, even UPS has quite a few large F-650 box trucks with the diesel. Obviously the Ford 6.7L is going to be limited to Ford products. Cummins has now products, just the engine, which they sell to anyone. The second water pump on the 6.7L handles more than just the cooler; its a low temp circuit for things like the trans cooler, intercooler, EGR cooler, etc. The Ford system has two radiators, two degas bottles, two water pumps, and four thermostats. Pretty impressive system. The water pumps are not set directly into the blocks; that way if the impellers wear a hole in the housing due to bearing failure you don't get coolant into the internal block, which seems pretty smart to me.